gdbstub initial code, v12

[Oleg Nesterov]

On 09/30, Oleg Nesterov wrote:
>
> Right now $G doesn't change FPU registers.

It turns out, $G can't even set the REGSET_GENERAL reg correctly.
I noticed this only because the tracee sometimes dies during the
single-stepping inside the dynamic linker. Indeed, $G passes the
wrong fs_index==0 to genregs_set().

> Next: watchpoints.

While trying to understand what does this mean, I hit another bug
in ugdb. A multithreaded tracee can "hang" if gdb simulates
watchpoints with single-steps + mem-fetch/compare. Still can't
understand why this happens, this should be resolved. This never
happens if the tracee is single-threaded.

Oleg.